Cytokines, the integral arm of bidirectional communication between the immune and central nervous systems, are also constitutive components of the hypothalamus where they may act as interneuronal signals. Our results indicate the existence of a communication link between the cytokine, Interleukin-1 (IL-1) and certain neuropeptides in the hypothalamus suggesting that the neuroendocrine and behavioral effects of cytokines may be mediated by these neuropeptides. We will test the hypothesis that the effects of cytokines on luteinizing hormone-releasing hormone (inhibition) and on corticotropin-releasing hormone (stimulation) are mediated by cytokine-induced upregulation of hypothalamic tachykinins and down- regulation of neuropeptide Y (NPY); furthermore we suggest that steroids restrain, whereas steroid deficiency, produced by peripheral action of cytokines, accentuates these central cytokine-neuropeptide interactions. This two-part hypothesis will be tested in 5 specific aims: Aim 1 is to identify the effective cytokines and demonstrate specificity of action in evoking cytokine-induced CRH and LHRH responses. In Aim 2 we will utilize antagonists to identify the tachykinin receptor subtypes and document tachykinin involvement in mediating the IL-1beta-induced neuroendocrine responses. Additionally, we will analyze the 3 species of preprotachykinin mRNAs in order to evaluate translational activation by IL-1beta. Aim 3 is to determine the effects of a chronic increase in central IL-1beta on tachykinin release in vivo and on gene expression. Aim 4 is to examine the effects of increases in peripheral cytokines on these hypothalamic interactions with the assumption that peripheral endotoxin stimulated IL- 1beta production in the hypothalamus, in turn, upregulates the central tachykinins. In accordance with the second part of our hypothesis, these proposed studies will be conducted in intact, castrated and testosterone- replaced male rats to decipher the role of gonadal steroids in modulating these hypothalamic interactions. Finally, in Aim 5 we plan to investigate the second putative aspect of cytokine action, viz. down-regulation of the excitatory peptide NPY. The acute and long-term effects of IL-1beta on NPY release in vivo and on gene expression in varied gonadal steroid environments will be studied. To accomplish these goals, release rates of the tachykinins, IL-1beta and NPY will be measured in vivo via the push- pull cannula and in vitro with short term hypothalamic cultures. To evaluate synthesis of the three classes of peptides, specific mRNA species will be quantitated by solution hybridization/RNase protection assay and the mRNAs localized in the hypothalamus by in situ hybridization; specificity of action will be demonstrated with specific tachykinin and IL-1beta receptor antagonists. The results of our investigations should establish (a) the intermediary role of the nociceptive tachykinins and of NPY in the hypothalamus and (b) the protective role of steroids underlying the neuroendocrine effects of cytokines. Because the cytokines, tachykinins and NPY are widely distributed in the brain, we envision that the knowledge of cytokine-neuropeptide interaction gained from these studies will aid in deciphering the devastating progression of neurodegeneration caused by inappropriate expression of cytokines in the brain due to chronic inflammatory diseases.